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The Definition of Quantities, Units, & Dimensions in Physics Measurement
Measurement is the process of comparing the value of a measured quantity with a similar quantity used as a unit. The result of this measurement is called a quantity. In physics, a quantity is something that can be measured and expressed with numbers and values that have units. With the quantity, you can do calculations properly and in a structured manner.
Definition of Quantity
Quantity is an important concept in physics. Quantity is anything that can be measured and expressed in value. Quantity can be expressed simply such as length or mass or more complexly such as energy, momentum, or electrical voltage. Quantity is usually expressed in certain numbers or numeric quantities. Components that are classified as quantities include:
- Length
- Mass
- Time
- Temperature
- Speed
- Force
- Energy
- Electricity
In physics, quantities are known to be two, namely basic quantities (fundamental quantity) and derived quantities (derived quantity). Basic quantities are basic or fundamental quantities that cannot be further broken down into other quantities.
Basic quantities have basic units associated with them in the system of units used. For example, the measurement of length in the International System of Units (SI) is meters. Meanwhile, derived quantities are quantities that are produced from a combination of basic quantities through mathematical operations such as addition, subtraction, multiplication, or division.
Derived units are obtained by combining basic units according to the underlying mathematical formula. Examples of derived quantities are speed measured as meters per second (m/s), kinetic energy is measured in joules, acceleration is measured in meters per second squared (m/s²).
Definition of Units
A unit is a value used to measure a quantity. Units are useful for providing a basis for comparing different quantities. In physics, there are units that have been established internationally or the International System of Units (SI). The purpose of creating SI is for universality. Examples of international units include:
1. Standard Unit of Length (m)
The unit of length based on the Systeme Internationale Unites (SI) is expressed in meters (m). The beginning of this standard unit of length was when the metric system was introduced, at that time the meter unit was proposed to be equivalent to one ten millionth of a quarter of the earth’s longitude that passes through the city of Paris.
However, scientists denied this theory because of the uncertainty in its calculations. Therefore, experts considered that the standard meter was less accurate because it was easily changed. Experts then re-established a length benchmark whose value was always constant.
2. Standard Unit of Mass
The standard unit for mass is Kg (kilogram). Initially, one standard kilogram was a mass for a metal cylinder made of platinum iridium stored in Sevres, France. The platinum iridium cylinder is 3.9 cm in diameter and 3.9 cm high. The mass of 1 standard kilogram at a temperature of 4°C is close to the mass of 1 liter of pure water.
3. Standard Unit of Time
The SI unit of time is s (second). Initially, 1 second was set equal to 1/86400 of the average apparent motion of the sun around the Earth. It turned out that the time set was not quite right because of the shift, so that the time could not be used as a benchmark. Then in 1956 it was re-established that one second is the time required for a cesium-133 atom to vibrate, which is 9,192,631,770 times.
4. Standard Unit of Electric Current
The standard unit of electric current is A (ampere). A (One ampere) is a unit of electricity which is often abbreviated as amp. This unit itself is taken from the name of one of the electromagnetism pensioners, namely André-Marie Ampère.
One ampere is an electric current that can flow from the negative pole to the positive pole, then between the two straight conductors with infinite length, with a negligible cross-section, and each placed in a separate place with a distance of one meter in a vacuum and produces a force of 2 × 10-7 newtons per meter.
5. Standard Unit of Temperature
Temperature indicates the degree of heat in an object. The standard unit of temperature itself is K (kelvin). K (Kelvin) is an absolute temperature unit in thermodynamics which is equal to 1/273.16 1 of the triple point temperature in water. The triple point itself states the temperature and pressure when there is a balance between vapor, liquid, and solid in a material. When compared to the scale on the Celsius thermometer, the triple point of water is 273.16 K and 611.2 Pa.
6. Standard Unit of Light Intensity
In SI (international units) light intensity has cd (candela units), which is the same as the intensity of a light source that can emit monochromatic radiation with a frequency of Hz. CD (candela) has a radiation intensity of 1/683 watt/steradian in a certain direction.
7. Standard Unit of Amount of Substance
In international units (SI) for the amount of substance, namely mole. One mole is proportional to the total amount of substance containing elementary particles whose number is the same as the number of atoms in kg of carbon-12. Elementary particles are fundamental elements that can form matter in the universe. These particles can include atoms, electrons, molecules, and others
Definition of Dimension
Another important term in physics is dimension. Dimension shows the mathematical aspect of a quantity. It should be noted that each quantity has a unique dimension. Each dimension reflects the relationship of the quantity to its basic units. In physics, there are three basic dimensions that are often used, namely length (L), mass (M), and time (T).
These dimensions can be used to assist in mathematical analysis and the preparation of physics formulas. The use of dimensions helps physicists check the mathematical consistency of physics formulas. For example, to calculate speed, the dimensions of the results of this calculation must match the dimensions of speed, namely distance/time.
The Importance of Quantities, Units, and Dimensions in Physics Measurement
Accuracy and Consistency: Using the right quantities, units, and dimensions can ensure that measurements and calculations in physics are carried out in a consistent and accurate manner.
Scientific Communication
Standardized units and dimensions allow scientists to understand and compare research results with each other.
Validation of Physics Equations
Dimensional analysis helps in checking the correctness of physics equations. If the dimensions on both sides of an equation are not the same, then the equation is wrong.
Simplification and Understanding
The concepts of quantities, units, and dimensions help simplify complex concepts in physics, making them easier to understand and apply.
